This invention relates to a heat transfer material. More specifically, this invention relates to a heat transfer material which can be suitably used for a heat transfer printer employed in a ticket vending machine or the like.
Recently, heat transfer printers have been widely used as output units of word processors, facsimile machines, personal computers, duplicating machines, ticket vending machines or the like.
As a heat transfer material for a heat transfer printer, generally used is a material comprising a substrate, a heat-meltable ink layer provided on one side of the substrate and a heat-resisting layer provided on the other side of the substrate.
In the printing system having a heat transfer printer, a printed image is obtained as follows: A heat-meltable ink layer of a heat transfer material is placed in contact with a sheet of plain paper. And then the side of the heat transfer material on which a heat-resisting layer is provided is heated by a thermal head or the like so as to melt the heat-meltable ink layer and transfer the ink to the plain paper.
Heat transfer printers are used as output units for word processors, facsimile machines, personal computers, duplicating machines, ticket vending machines or the like. A ticket vending machine has a mechanism for conveying ticket paper after printing. Many ticket vending machines also have a mechanism for detecting the heat transfer material using a near infrared ray (the above mechanism is hereinafter referred to as "near infrared ray detector").
In the mechanism for conveying ticket paper, necessary pairs of rolls facing with each other rotate and ticket paper is conveyed between the facing rolls. Generally, one of the facing rolls is made of rubber and the other is made of metal. The printed side of the ticket paper generally touches the metal roll.
Since the ticket paper sometimes fails to be conveyed properly when the pressure of the rubber roll on the metal roll is low, relatively high pressure is applied. Thus, the heat-meltable ink on the printed side of the ticket paper is transferred to the metal roll to form stains on the metal roll (hereinafter referred to as "roll stain"). In case of a ticket vending machine in which thousands of pieces of ticket paper are printed in a day, the unprinted portion of the ticket paper is stained on account of roll stain.
It has been found that roll stain can be prevented from occuring by reducing the coating weight of the heat-meltable ink layer. The reason is that most of the heat-meltable ink is soaked into the plain paper when the coating weight is small. When the coating weight is large, a considerable amount of the heat-meltable ink which remains on top of the plain paper, not soaked therein, is transferred to the metal roll to form roll stain.
As described above, roll stain can be prevented from occuring by reducing the coating weight of the heat-meltable ink layer.
However, when the coating weight of the heat-meltable ink layer is reduced, the absorbance of visible rays and the absorbance of near infrared rays are both lowered. If the absorbance of near infrared rays is too low, the heat transfer material cannot be detected by a near infrared ray detector employed in a ticket vending machine.